Group Iv drugs slow phase 4 spontaneous depolarization and slow conduction in tissues dependent on calclum currents, such as AV node. 2 (4) Class IV Ca2+ channel ockers verapamil维拉帕米 Outside K currents Action potential Verapamil, diltiazem and nifedipine block open or inactivated calcium channels(4) Class IV Ca2+ channel blockers verapamil 维拉帕米